SIVMAC vaccine studies using whole inactivated virus antigen sequentially depleted of viral proteins

Groups of four rhesus monkeys were immunised at 0, 1, 2, and 13 months with whole inactivated SIV_mac32H, SIV_mac depleted of the outer envelope glycoprotein gp130, virus cores depleted of the lipid membrane (and hence transmembrane glycoproteins), or purified gag protein. These macaques plus controls were challenged with either the homologous SIV_mac251–32H. grown in human cells or the same virus passed once through monkey cells. None of those challenged with monkey-grown virus were protected, whereas all in the whole and gp130-depleted virus groups, and one in the core group resisted challenge with human-grown virus. As the only difference between the challenge viruses was a single in vitro passage in monkey cells it can be concluded that protection was solely due to human cell components. Finally, passive transfer of high titer IgG from monkeys infected with the homologous challenge virus failed to protect monkeys from infection despite the presence of circulating neutralising antibodies.